This invention relates to an exhaust tube mounting apparatus for an outboard motor.
In outboard motors, a powerhead is secured to the upper end of a drive shaft housing and a lower propeller unit is secured to the lower end of the drive shaft housing. Generally, the engine exhaust is directed downwardly through a tube system within the drive shaft housing to discharge the exhaust gases at or beneath the waterline, and preferably through the propeller unit. For higher horsepower engines, a pair of exhaust tuning pipes will be secured to the powerhead for the banks of alternately fired cylinders and each extended downwardly into the drive shaft housing. An exhaust tube is generally secured in sealed relationship extended through the drive shaft housing to direct the exhaust gases downwardly to the lower unit, to separate the exhaust passageway from the other components within the drive shaft housing and the like.
The exhaust tube defines an expansion chamber within which the tuning exhaust pipes terminate and around which a cooling and sound deadening water area may circulate. Thus, normally a water cooling tube, as well as a shift mechanism may be located within the drive shaft housing for coupling between the various functional components.
The exhaust tube has generally been extended through the upper end of the drive shaft housing structure and secured to the lower adapter plate. The lower end of the exhaust tube extends downwardly from the drive shaft housing into sealing engagement with a suitable sealing retainer means in the lower propellor unit. Although such structures provide a completely satisfactory functional system, the lower unit must be very carefully interconnected to the drive shaft housing to ensure the necessary alignment for establishing a firm and reliable sealing of the exhaust tube to the discharge passageway in the lower unit.